Gale Warning 369, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 PM AKDT Sat Apr 30 2022

.ANALYSIS AND UPPER LEVELS...

A broad upper low centered near Sand Point will drive several
systems through the Gulf in the coming days. The current
associated surface low is tracking well south of Kodiak Island,
however its front extends well to the north and is bringing
moderate rain and gusty easterly winds to Kodiak City and through
the Kamishak Gap. Widespread showers are also seen along the
eastern Kenai Peninsula and Prince William Sound. Higher terrain
will see significant snowfall, with snow levels rising to around
1500 ft during daytime hours. The swath of moisture extends all
the way into the central Pacific. Aided with a deep southerly
500 mb flow, QPF amounts will likely be on the higher side of
guidance. Satellite indicates mostly cloudy skies over much of the
interior, but precipitation remains mostly confined to the coast.
Light rain is occurring across Bristol Bay, with showers extending
into the Kuskokwim Delta. The Bering Sea/Aleutians remain quiet
as a low weakens west of Unalaska.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement into early next week.
Shortwaves will allow for precipitation chances over Southcentral
late Sunday into Monday although the exact timing is still uncertain.
Confidence is high that the general active pattern will continue
through at least mid week with an upper low slowing near Kodiak.

&&

.AVIATION...

PANC...VFR conditions will persist. Although gusty winds are
expected along Turnagain Arm, winds over the terminal should
remain generally light as the Turnagain Arm winds bend
southward down Cook Inlet toward low pressure in the Gulf.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tonight through Monday
night)...

An unseasonably strong low is quickly moving into the Gulf this
evening with its front just grazing the southern Kenai Peninsula
this afternoon. Storm force winds are expected to develop along
the northern Gulf Coast as the front pushes against and parallels
the terrain. The system has developed along the left exit region
of a 110 to 125 kt jet stream, which is tapping moisture from as
far south as 38N latitude. The E-W orientation of the front as it
approaches and a deep moisture fetch will bring a considerable
amount of rain to Whittier, Portage, Girdwood and Turnagain Pass
through Sunday afternoon before it weakens. The Seward area will
have much lighter rain during this time period due to strong
easterly winds helping to downslope the fjord. Elevations above
1500 ft to 1800 ft will receive a considerable amount of snow,
with multiple feet of heavy wet snow possible, particularly near
Turnagain Pass and Portage. The mountains surrounding Valdez and
Thompson Pass will get some snow as well, but overall this frontal
orientation and upper level dynamics are less conducive for heavy
snow in the area.

The surface low for this system will remain off the east coast of
Kodiak Island through Sunday afternoon before the parent trough
lifts northward. Expect heavy rain and winds to continue over
Kodiak through Sunday morning, before a wind shift to the west
help to dry things out by Sunday afternoon. The wind shift in
Kodiak will also have an accompanying shift to the south in
Seward, which will bring a heavier period of rain overnight
Sunday into Monday morning.

For the main population centers, most of the region will remain
downsloped for the majority of the event, with the exception of
the Homer area and Anchor Point, which will likely have some
light rain bleeding over the mountains. As the trough lifts
north Sunday afternoon, chances of rain become possible for the
population centers as downsloping may be overcome by the mid to
upper level lift. With the moderate downsloping winds still in
place, any rain that does reach the surface should be light.
Moisture will also have to overcome dry air at and near the
surface.

On Monday another system will move into the Gulf, offering little
to no break in rain for coastal areas with more upper elevation
snow. By this time the upper level dynamics are less supportive
of a strong system as the jet moves south of the area, but a
broad upper level low is expected to develop and become centered
over the Alaska Peninsula Monday and drift east into the western
Gulf on Tuesday. This broad low will continue to send weak
southerly shortwaves into Southcentral with overall cloudy
conditions near the coast and partly cloudy skies inland.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Tonight
through Monday night)...

There is a stalled frontal boundary from the Kuskokwim Delta to
Kodiak. At 500 mb there is a closed low over Bristol Bay and the
Pribilof Islands with a major shortwave near Dutch Harbor and a
major shortwave south of the Alaska Peninsula. The energy that is
south of the Alaska Peninsula will recurve and move northwestward
towards King Salmon tomorrow. Meanwhile there is another closed
low over the Western/Central Aleutians will push eastward
absorbing the remnant energy from the leading closed low. Expect
another round of showers. The lion's share of the precipitation
is expected along the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3 -
Tonight through Monday night)...

A 967 mb mature low in the NW Pacific will reach Atka at 980 mb
Sunday afternoon. This system is being driven my a 150 knot jet
core. This system is already past its prime, but expect small
crafts and possibly pockets of gale force along the western and
central Aleutian chain. Cool northerly flow will follow in the
wake of the frontal passage. The ice shield has retreated and is
near St Matthew Island.

&&

.Marine (Days 3 through 5: Tuesday through Thursday)...

Gulf of Alaska: Gales linger along the north Gulf coast through
Tuesday morning. High confidence that winds will be sub-gale from
Tuesday morning through Thursday. Seas up to 18 feet diminish to
12 feet and lower by Tuesday afternoon.

Bering: High confidence in sub-gale winds through Thursday. Seas
below 15 ft.

&&

Long Term Discussion (Days 4 through 7: Wednesday through
Saturday)...

An active pattern with unsettled weather conditions will be in
store through the long term period. On Wednesday, a broad upper
level trough extends over the state. An Arctic low developing over
the northern Bering moves southward, reaching the Aleutians for
Thursday. This low has the potential to bring gusty winds and
precipitation to the Pribilof Islands and central Aleutians. Over
Southcentral, a weak low centered over the Gulf keeps clouds and
scattered showers in place across much of the coast and interior
Southcentral. By late Friday, the Bering low crosses the Aleutian
Chain to the south and gradually meanders eastward into the Gulf
and eventually dissipates. By the weekend, a significantly more
amplified pattern takes shape as a broad upper level Siberian
ridge begins to build eastward over the Bering late Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 119 120 131.
         Gale Warning 125 130 132 137 138 139 140 150.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AP
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PS
MARINE/LONG TERM...KC